How Humid is Too Humid?

[Mark Duksta]

Hello All,

I need to shoot some shellac on a project I'm trying to complete and the weather won't cooperate.

What is the highest humidity I can spray shellac?

I don't want to deal with blushing at the very end of the project.

Thanks,

Mark

[Scott Holmes]

Try it and see shellac is pretty tolerant. Remember the perfect shellac coat is the thinnest possible coat that is flawless.

Don't be tempted to build it up thick like varnsih or lacquer.

[Henry Ambrose]

I don't think it ever gets too humid in Austin for spraying shellac.
(seriously)

[Ed Edwards]

Scott,

Please expand on"the thin coat and don't be tempted to build it thick".
I'm always trying to learn more about this wacky finishing world
Thanks,Ed

Remember the perfect shellac coat is the thinnest possible coat that is flawless.

Don't be tempted to build it up thick like varnsih or lacquer.

[Mark Duksta]

Henry,

The humidity around here the last couple of weeks has generally been around 70% or above with one or two dry days down to around 50% or 60%. The next week's forecast shows that the humidity is to be 80% and above. There is one day that it should get down to about 60%. So you think it's safe to shoot on any one of those days?

[Scott Holmes]

I use shellac in Houston (more humid than Austin) all the time; not really an issue.

[Scott Holmes]

Shellac should be a VERY thin finish. If you build it up thick it will alligator. Ever seen an old piece of furniture and the finish looks like alligator hide? Too much shellac.

For clocks and decorative items sheallac is an excellent choice. I use shellac, very often; usually as a seal coat over a color step or as a barrier coat between finishing steps... It is fast drying, very hard, optically clear and color fast (it will not get darker with age).

Varnish, waterborne and lacquer finishes can be built up to a thicker coat. They can look PLASTIC when built too thick, but they don't alligator like shellac.

[Howard Acheson]

The biggest problem when spraying finishes like lacquer and shellac with their fast evaporating solvent is blush. This is caused by the fast evaporation of the finish rapidly cooling the wood and air at the surface and creating condensation in the finish. You can see it as a white fog in the finish. Using a turbine type HVLP set up will create a bigger problem. The turbine heats the air and condensation is more readily produced. You can pad on some alcohol which will allow the condensation to escape. You can also add a retarder to finish. A tablespoon of gum turpentine added to a quart of shellac will generally work. Or, you can go to Jeff Jewitt's site (www.homesteadfinishingproducts.com) and he can sell you some shellac retarder.

[Mark Duksta]

Scott, It's good to know you're in Houston and you're not having any blushing issues. That puts it in perspective.

Howard, Shellac retarder. That's sounds like something I want to try. Thanks. The shellac I'm using came from Homestead.

I haven't had any issues with shooting shellac, but I always wait for a very dry day. Lately there have been no dry days.

Thanks,

Mark

[Henry Ambrose]

Henry,

The humidity around here the last couple of weeks has generally been around 70% or above with one or two dry days down to around 50% or 60%. The next week's forecast shows that the humidity is to be 80% and above. There is one day that it should get down to about 60%. So you think it's safe to shoot on any one of those days?

Your question is well answered - and, yes, I'd spray shellac under those conditions without a second thought. What Scott is saying about keeping the coat thin is a great suggestion.

[Scott Holmes]

Guess I aught mention that my shop is heated and air conditioned. That helps with humidity quite a bit.

[Jason Roehl]

I've sprayed shellac in humid conditions on hot, warm and cool days (in an open garage or in the shade) without blushing issues.